|Quadrangle map, 1:250,000-scale||TL|
|Quadrangle map, 1:63,360-scale||C-4|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||Reed and others (1978, locality 27) show this occurrence in the northwest quarter of Section 13, T. 30 N., R. 14 W., of the Seward Meridian on a northerly tributary of the Yentna Glacier at about 3300 feet in Denali National Park and Preserve.|
Disseminated chromite in mafic and ultramafic rock cut by thin veinlets of magnetite and minor amounts of sulfides were noted by Cobb and Reed (1980) at this locality.
This is one of several chromite occurrences in a 25-mile long belt of alpine-type ultramafic bodies described by C.C. Hawley and Associates, Inc. (1978, Fig. 4.1-(C)3 and Fig. 4.0-B), as part of the Dall Trend, that are discontinuously exposed from the Dall Glacier northeast to the Lacuna Glacier. These chromite- and magnetite-bearing dunite and peridotite sills are shown by Reed and Nelson (1980) in a narrow belt of middle to upper Paleozoic sedimentary rocks that are exposed between the middle Tertiary (38 m.y.) Foraker pluton and the northwest-trending fault which places the Paleozoic rocks over the Mesozoic marine sedimentary rocks (KJs). Foley and others (1997, p. 431) suggest that these ultramafic bodies may be genetically related to the composite plutons (Tcp) of Reed and Nelson (1980) in the upper Yentna River.Reed and others (1978) describe these occurrences as magmatic segregations of podiform and disseminated chromite hosted in dunite sills. Chromite occurs as disrupted, irregular pods of various shapes, as much as 6 feet thick and 60 feet long, and as disseminations and streaks throughout the dunite. Other chromite occurrences in this trend are described in TL 02, TL003, TL008 - 011, and TL 055.
|Geologic map unit||(-151.822245807557, 62.6914544090542)|
|Mineral deposit model||Podiform chromite (Cox and Singer, 1986; model 8a).|
|Mineral deposit model number||8a|
|Age of mineralization||Mesozoic and (or) Paleozoic (Reed and Nelson, 1980) or Late Cretaceous/early Tertiary (?) (Foley and others, 1997).|
|Workings or exploration||Reconnaissance mapping, stream silt and rock sampling are all that have been done here. Chromium content of 0.7 to 1% from typical dunite is given in Reed and others (1978). The average of 3 microprobe analyses of one sample was 58.4% Cr2O3, 21.1% FeO, 8.9% MgO, and 9.7% Al2O3.|
|Indication of production||None|
Additional commentsMineral occurrences in the Dall Trend are all within Denali National Park and Preserve.
C.C. Hawley and Associates, Inc., 1978, Mineral appraisal of lands adjacent to Mt. McKinley National Park, Alaska: U.S. Bureau of Mines Open-File Report 24-78, 277 p., 12 sheets.
Cobb, E.H., and Reed, B.L., 1980, Summaries of data on and lists of reference to metallic and selected nonmetallic mineral deposits in the Talkeetna quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-884, 106 p.
Foley, J.Y., Light, T.D., Nelson, S.W., and Harris, R.A., 1997, Mineral occurrences associated with mafic-ultramafic and related alkaline complexes in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 396-449.
MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000.
Reed, B.L., and Nelson, S.W., 1980, Geologic map of the Talkeetna quadrangle: U.S. Geological Survey Miscellaneous Investigations Map I-1174, 1 sheet, scale 1:250,000.
|Reporters||Madelyn A. Millholland (Millholland & Associates)|
|Last report date||8/10/1998|